Most desktop personal computer (PC) systems contain "expansion bus" slots. These slots are physical connectors that allow printed circuit board (PCB) cards containing additional resources to be connected to the PC. Examples of typical expansion card functions are: disk drive controller, video graphics controller, serial port controller, parallel port controller and network controller. Each expansion card that is inserted into the system is connected to the PC's main resources (such as memory and the central processing unit (CPU)) through the expansion bus. Since the expansion bus is shared by all cards in the system, any card that wishes to utilize the PC's main resources must first indicate its intentions by asserting a "DMA request" signal. Alternatively, whenever the PC's CPU wishes to access resources on board an expansion bus card, it must uniquely indicate this to insure that only one card responds. This is done through unique "I/O and memory addressing." Any expansion card may request attention from the CPU by asserting an "interrupt" signal.
When several expansion cards have been installed in a system, then there should not be conflicts between cards with respect to the DMA request, the I/O and memory addresses, and the interrupt signalling. If conflicts do arise, the system will fail. To avoid this problem, the system provides multiple DMA request lines, or channels, and each card that wishes to utilize the DMA resources must be connected to a separate DMA request channel to avoid conflicts. The system also provides multiple interrupt channels, and again, each card that wishes to utilize an interrupt must be connected to a separate interrupt channel. For I/O and memory addressing, expansion cards typically contain a fixed set of possible addresses, and the address for each card must be set to a value that does not conflict with the address of any other resource in the system.
The most common method for selecting a particular DMA channel for a card (or for selecting interrupt channels and addresses) is to build "jumpers" onto each expansion card. The jumpers are manually moved in order to vary the selected DMA request and interrupt channel selection and also to select different I/O and memory addresses for the card to respond to. Physically, each card is connected to multiple channels at the expansion bus connection point; these signals are all connected to one side of a multiplexer that is controlled by the jumper settings. By modifying the jumper settings, different DMA channels and interrupt channels can be selected. In the case of I/O and memory addressing, the jumpers are used to modify the decoder that determines when an address that is present on the expansion bus corresponds to the card's address. Modifying the I/O and memory address jumpers modifies the address to which the card responds.
While using jumpers to create flexibility for each card allows multiple cards to be inserted into a system without conflict, the procedure that must be followed when inserting new cards is such that the system must be powered off in order to readjust the jumper settings on the existing cards to make room for the new card. Then the system is powered up again and for those cards that have modified jumper settings, individual "card resource files" must be updated so that the driver software for each card is informed of the changes.
There have been other attempts to solve this problem. However these solutions do not provide an adequate degree of protection for many applications or are very complex to implement. Hence, there is a long-felt but unsatisfied need to have a system for providing a reliable system for relocating expansion cards without having to physically make adjustments to the card or the computer in which the card is located. The present invention addresses such a need.